Residential and commercial alarm systems typically report events (including alarms) using a phone line connection to the central station. In traditional installations, the event data is sent through a combination of tones and data over the phone line to a DACR (digital alarm communication receiver) located at the central station.
Recently, alarm panels have begun to provide voice communication capabilities, whereby at the end of the event transmission, the alarm panel signals the DACR that it will not disconnect, and the DACR should connect the incoming telephony path to an attendant. At this point, the attendant, via DTMF commands, can establish a one-way or two-way voice path with the alarm panel.
This feature has proven to be very useful for alarm verification, as well as for use in PERS (Personal Emergency Response System) installations. However, it does present difficulties for cellular alarm communications. If the voice channel is used to transmit the security signaling directly to the alarm receiver at the central station, then the signaling may not work well, as telephony facilities at central stations, as well as the alarm receivers themselves, vary widely in quality, and the cellular signal imparts its own, sometimes significant, distortion.
Previous inventions have discussed separating the security signaling and the voice at the alarm premises, sending the security signaling over a dedicated data channel such as SMS or GPRS, and rejoining the signaling and voice at the alarm communication center. This approach, however, can lead to delays, since SMS transit time is multiple (sometimes many) seconds, and GPRS sessions may sometimes be unavailable.